Perfluoride processing apparatus

ABSTRACT

A plurality of etchers such as poly-etchers  3  or the like are installed within a clean room  2 . A duct  7  that is connected to all the etchers is connected to a PFC decomposition device  9 , which is installed outside of the clean room  2 . An exhaust gas which contains PFC as drained out of all the etchers within the clean room  2  is supplied by the duct  7  to the inner space of PFC decomposition device  9 . After having heated up within the PFC decomposition device  9 , the PFC is decomposed by the action of a catalyst which is filled within the PFC decomposition device  9 . It is no longer required to provide a space for installation of the PFC decomposition device  9  in the clean room  2  with the semiconductor fabrication apparatus or the liquid crystal manufacturing apparatus installed therein, thus enabling size reduction or “downsizing” of the clean room. It is possible to reduce the size of a clean room in which a semiconductor fabricating apparatus or a liquid crystal manufacturing apparatus is installed.

The present application is a continuation of application Ser. No.10/245,491, filed Sep. 18, 2002, now abandoned, the entire disclosure ofwhich is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to perfluoride processingapparatus and, more particularly, to perfluoride processing apparatussuitable for use during processing of perfluoride-carbon orperfluocarbon (PFC) gases which generate in semiconductor fabricationprocesses and liquid crystal manufacturing processes or the like.

2. Prior Art

In the semiconductor fabrication and liquid crystal manufacturingprocesses, PFC gases are used as an etching gas of semiconductor andliquid crystal materials, a cleaning gas of etchers, and a cleaning gasof chemical vapor deposition (CVD) equipment. However, PFC gases are theones that are extremely significant in anathermal coefficient to anextent that it is ten thousand to several thousand times greater thanthat of CO₂. From a viewpoint of production efficiency withoutconsumption of a total amount of PFC gas, the currently availablesemiconductor/liquid-crystal manufacturing processes are designed sothat after having consumed 20 to 50% of the gas, the remaining PFC gasis exhausted and drained out of an etcher (or CVD equipment) as anexhaust or waste gas. For the purpose of precluding anathermalization ofthe Earth, it is required to perform PFC gas decomposition processing tothereby prevent the PFC gas from being released to external environment.Note that representative examples of the PFC gas include, but notlimited to, CF₄, CHF₃, C₂F₆, C₃F₈, C₄F₆, C₅F₈, NF₃, and SF₆.

In order to suppress outward release or emission of PFC gases toexternal environment, it has been known in semiconductor and liquidcrystal manufacturing industries that as disclosed in JapaneseApplication Patent Laid-Open Publication No. Hei 11-319485,perfluocarbon decomposition devices (referred to as PFC decompositiondevices hereinafter) are installed in units of PFC gas-use etchers sothat each is adjacent to its associated etcher, wherein a catalyst isused to perform decomposition processing of a PFC gas in exhaust gasesas drained out of the etchers. This PFC decomposition device is equippedwith a reaction unit which is filled with a PFC decomposing catalyst, asilicon component removing device which removes silicon componentscontained in an exhaust gas to be supplied to the reaction unit, acooling chamber for cooling or refrigerating the exhaust gas thatcontains therein decomposition gas of the PFC as decomposed by thecatalyst, and further an acidic gas removing device for removing anacidic gas contained in the exhaust gas as drained out of the coolingchamber. A catalyst-using PFC decomposition device is also disclosed inJapanese Application Patent Laid-Open Publication No. Hei 11-70322.

As the silicon component removing device, the cooling chamber and theacidic gas removing device require the use of water, it is a must toconnect a water supply pipe to the individual PFC decomposition device.In view of the fact that each PFC decomposition device is installedwithin a clean room, respective water supply pipes being connected tothem also are installed in the clean room. Water drain pipes also areconnected to the PFC decomposition devices respectively. Due to this,part of the inner space of the clean room is to be occupied by therespective PFC decomposition devices and the water supply/drain pipesassociated therewith. In case a clean room is newly formed withsemiconductor fabrication apparatus (or alternatively liquid crystalmanufacturing apparatus) such as a plurality of etchers installedtogether therein, a need is felt to acquire within the clean room aninstallation space of a plurality of PFC decomposition devices and avariety of types of utility equipment (such as water supply pipes andwater drain pipes or the like) associated therewith, which would resultin the space within the clean room being enlarged accordingly.Alternatively, in the case of installation of one or more PFCdecomposition devices within the currently established clean room, itsometimes happen that the semiconductor fabrication apparatus (or liquidcrystal manufacturing apparatus) such as etchers which have beeninstalled within the clean room must be moved in order to acquire theinstallation space of the PFC decomposition devices and various types ofutility equipment.

Because of the installation of a variety of types of utility equipmentwith respect to each PFC decomposition device within the clean room, ittakes much time to install these facilities.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide aperfluoride processing apparatus capable of relatively reducing the sizeof a clean room and also a perfluoride processing method.

A principal feature of the present invention which attains the foregoingobject lies in that it comprises an exhaust gas pipe connected to aplurality of semiconductor fabrication apparatuses installed within aclean room with perfluoride supplied thereto for permitting flow of anexhaust gas containing therein said perfluoride as drained out of thesemiconductor fabrication apparatuses, and a perfluoride decompositiondevice connected to said exhaust gas pipe and installed outside of saidclean room for decomposing said perfluoride as contained in said exhaustgas to be guided by said exhaust gas pipe.

In accordance with this invention, it is no longer required to acquireany extra space for installation of more than one perfluoridedecomposition device within the clean room, which in turn makes itpossible to reduce in size or “downsize” the clean room. In particular,in the case of application to the currently established clean room also,it is no longer necessary to acquire the installation space of suchperfluoride decomposition device(s) within the clean room; thus, itmakes it unnecessary to move the semiconductor fabrication apparatuswithin the clean room in order to perform installation of suchperfluoride decomposition device(s).

A principal feature of the present invention which is applied to liquidcrystal manufacturing architectures lies in that it includes an exhaustgas pipe connected to a plurality of liquid crystal manufacturingapparatuses installed within a clean room with perfluoride suppliedthereto for permitting flow of an exhaust gas containing therein saidperfluoride as drained out of the liquid crystal manufacturingapparatuses, and a perfluoride decomposition device connected to saidexhaust gas pipe and installed outside of said clean room fordecomposing said perfluoride as contained in said exhaust gas to beguided by said exhaust gas pipe. In this case also, it is no longerrequired to acquire any extra space for installation of more than oneperfluoride decomposition device within the clean room, which in turnmakes it possible to downsize the clean room. Especially in the case ofapplying to the currently established clean room also, it is no longernecessary to acquire the installation space of such perfluoridedecomposition device(s) within the clean room; thus, it makes itunnecessary to move the liquid crystal manufacturing apparatus withinthe clean room in order to perform the installation of such perfluoridedecomposition device(s).

Preferably the perfluoride decomposition device is equipped with areaction unit in which a catalytic layer is provided and to which anexhaust gas containing perfluorides is supplied and which decomposessaid perfluorides, and an acidic substance removing device which removesany reactive products as produced by chemical reaction with Ca salts ofthe acidic substance that is contained in the exhaust gas drained out ofthe reaction unit. The use of this perfluoride decomposition devicecauses the acidic substance being contained in the exhaust gas to beremoved away as reactive products producible through reaction with Casalts. Thus, no waste water generates from this perfluoridedecomposition device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a configuration of PFC processing apparatusin accordance with one preferred embodiment of the present invention;

FIG. 2 is a diagram showing a detailed configuration of a wet-type PFCdecomposition device of FIG. 1;

FIG. 3 is a configuration diagram of another embodiment of the wet-typePFC decomposition device;

FIG. 4 is a configuration diagram of still another embodiment of thewet-type PFC decomposition device;

FIG. 5 is a configuration diagram of a PFC processing apparatus inaccordance with another embodiment of this invention;

FIG. 6 is a configuration diagram of a PFC processing apparatus which isanother embodiment of the invention with a dry-type PFC decompositiondevice applied thereto;

FIG. 7 is a detailed configuration diagram of a filter device of FIG. 6;

FIG. 8 is a configuration diagram of another embodiment of the dry-typePFC decomposition device; and

FIG. 9 is a configuration diagram of a further embodiment of thedry-type PFC decomposition device.

DESCRIPTION OF THE INVENTION Embodiment 1

Prior to explanation of a perfluoride processing apparatus, that is, PFCprocessing apparatus, in accordance with one preferred embodiment of thepresent invention, a schematic configuration of a semiconductorfabrication system including a semiconductor fabrication factory willfirst be explained with reference to FIG. 1 below. The illustrativesemiconductor fabrication system is equipped with a semiconductorfabrication factory, a PFC decomposition device 44, and a factory acidicgas processing equipment 46. The building 1 of semiconductor fabricationfactory has therein a clean room 2. A plurality of semiconductorfabrication apparatuses including etchers such as poly-etchers 3, anoxide film etcher 5, and a metal etcher 53 are installed within theclean room 2. Also installed within the clean room 2 is a plurality ofgas supply devices 48. The individual gas supply device 48 is the onethat supplies gases (such as PFC gas or the like) required at etchingand cleaning process steps to its corresponding etcher (i.e.semiconductor fabrication apparatus with PFC gas supplied thereto). Thegas supply device 48 is designed for example to internally have abuild-in cylinder or “bomb” receiving vessel (not shown) in which aplurality of bombs (not shown) that are filled with required gases.

The factory acidic gas processing equipment 46 comprises an acidic gasremoving device 47, a gas collection duct 49 and an exhaust duct 51. Thegas collection duct 49 is for connection between the space within thebomb-receiving vessel and the acidic gas removing device 47. The acidicgas removing device 47, which is installed out of the semiconductorfabrication factory building 1, is connected to the gas exhaust duct 51through a blower 50. Depending upon the type of etcher, an acidic gaswhich is supplied from a bomb is used for wafer etching processes. Whenthe acidic gas that is filled in the bomb leaks toward the outside bysome causes, the bomb-receiving vessel is operable to prevent the leakedacidic gas from flowing into the clean room 2. Such leaked acidic gas asfilled in the bomb-receiving vessel is driven by the blower 50 to reachthe acidic gas removing device 47 through the gas collection duct 49 andis then removed away at the acidic gas removing device 47. The remaininggas with the acidic gas removed away is drained out of an exhaustcylinder 52 via the exhaust duct 51.

The PFC processing apparatus 44 comprises a duct 7, a PFC decompositiondevice 9 and a gas exhaust duct 28. The PFC decomposition device 9 isinstalled outside of the clean room 2 and within (or alternativelyoutside of) a little house (not shown) which is built within the sitefor the semiconductor fabrication factory at a location that is outsideof the semiconductor fabrication factory building 1. The duct 7 is alsoconnected to the polyetchers 3, oxide film etcher 5 and metal etcher 53respectively, which are installed within the clean room 2, and is alsoconnected to the PFC decomposition device 9. An acid gas removing device4 is installed at the duct 7 at a position adjacent to a connectionportion with the polyetchers 3. Another acid gas removing device 4 isalso installed at the duct 7 at a position adjacent to a connectionportion with the metal etcher 53. A carbon monoxide removing device 6 isinstalled at the duct 7 at a position near a connection portion with theoxide film etcher 5. The exhaust duct 28 is connected to the PFCdecomposition device 9 through a blower 25 and also to the exhaust gascylinder 52.

A detailed configuration of the PFC decomposition device 9 will beexplained based on FIG. 2. The PFC decomposition device 9 includes apre-processing tower 10, a reactor 11, a cooling device 20, and anacidic gas removing device 22. The preprocessing tower 10 has a solidcomponent removing device 54 and a neutralizing tank 61 which isprovided at lower part of the solid component removing device 54. Sprays62, 63 are installed within the solid component removing device 54. Thereactor 11 has a heating unit 12 and a reacting unit 16. The heater unit12 is equipped with a heating device (for example, electric heater) 13and forms a space 14 for use as a gas passage on the inner side of theheater device 13. The reaction unit 16 has a heating device (e.g.electric heater) 18 and a catalytic layer 17 as installed inside of theheater device 18. In the reaction unit 16, a space 19 for use as a gaspassage is formed within the heater device 18 at a location overlyingthe catalyst layer 17. Upper part of the space 14 and upper part of thespace 19 are coupled together by a duct 15. The cooler device 20includes a spray 21 therein. Similarly the acidic gas removing device 22also includes sprays 23, 24 therein.

The duct 7 is connected via a three-way valve 8 to the solid componentremoving device 54. One exhaust port of the three-way valve 8 isconnected by a pipe 60 to the gas collection duct 49 at a location onthe upstream side of the acidic gas removing device 47. The three-wayvalve 8 is an exhaust gas flow path changeover device which switchesbetween the supplement of an exhaust gas to the solid component removingdevice 54 and the supplement to the pipe 60. The pipe 60 is a bypasspipe with respect to the PFC decomposition device 9. A pipe 26 connectstogether the solid component removing device 54 and the space 14 withinthe heater device 12. A space formed below the catalyst layer 17 withinthe reaction unit 16 is coupled by a pipe 27 to the cooler device 20.Upper part of the space within the cooler device 20 is coupled to theacidic gas removing device 22. The exhaust duct 28 is connected to theacidic gas removing device 22 at a location in on the upstream side ofthe blower 25. A water drain pipe 30 which is provided with a pump 29 isconnected to a bottom portion of the cooler device 20. A pipe 31 that isconnected to the water drain pipe 30 in the downstream of the pump 29 isconnected to the spray 24. A pipe 32 connects the pipe 31 and the spray21 together. A water drain pipe 37 in which a pump 36 is provided isconnected to a bottom portion of the neutralizing tank 61. A pipe 38which is connected to the water drain pipe 37 at a location in thedownstream of a pump 36 is connected to the spray 63. A water supplypipe 33 is connected to the spray 23. The water supply pipe 34 connectstogether the water supply pipe 33 and the spray 62. A water supply pipe35 is coupled to the space 14 within the heating unit 12. An alkali tank39 is connected to the neutralization tank 61 via a pipe 43 which isprovided with a pump 42 and is also connected to the cooler device 20 bya pipe 41 provided with a pump 40.

Supplied to the polyetcher 3 from its associated gas supply device 48are Cl₂, HBr, CF₄ (in some cases, CHF₃, C₅F₈, C₂F₆ or else). CO, CF₄ (insome cases, CHF₃, C₅F₈, C₂F₆, SF₆ or else) are supplied to the oxideetcher 5 from its associated gas supply device 48. Cl₂, BCl₃, CF₄ (insome cases, CHF₃, C₅F₈, C₂F₆ or else) are supplied to the metal etcher53 from its associative gas supply device 48. Respective one of theabove-noted gases are filled in separate bumps in corresponding gassupply devices 48 on a per-kind basis. Although part of each kind of gasas supplied to each etcher is consumed during wafer etching processes,the remaining gas will be drained out of each etcher as an exhaust orwaste gas. Within each etcher, HF that is an acidic gas is produced bydecomposition of PFC(CF₄) thus consumed therein. In addition to the HF,the exhaust gas contains by-products (SiF₄, WF₆ and the like) as hasbeen produced by reaction between wafer rare material as cut awaythrough etching and the PFC gas(es) along with solid components (SiO₂,WO₃ and others).

After removal of harmful acid gas (Cl₂) at the acid gas removing device4, the exhaust gas as drained out of the polyetcher 3 is introduced intothe solid component removing device 54 via the duct 7. After removal ofharmful gas (CO) at the carbon monoxide removing device 6, the exhaustgas drained out of the oxide film etcher 5 is introduced into the solidcomponent removing device 54 via the duct 7. After removal of harmfulacid gases (CO₂, BCl₃) at the acid gas removing device 4, the exhaustgas drained out of the metal etcher 53 is introduced into the solidcomponent removing device 54 via the duct 7. In cases where the PFCdecomposition device 9 properly functions, the three-way valve 8operatively couples together the etchers and the PFC decompositiondevice 9 to thereby ensure that the exhaust gas drained out of eachetcher can flow into the PFC decomposition device 9. Due to this, anyexhaust gas cannot flow from the duct 7 into the pipe 60. The exhaustgas as drained out of an etcher which uses no harmful gases is directlydrained out of this etcher to the duct 7.

Water which was supplied from the water supply pipe 34 is continuouslysprayed from the spray 62 into the solid component removing device 54.The exhaust gas to be supplied to the solid component removing device 54contains PFC (CF₄) and also impurities which generate solid componentsby reaction with water such as SiF₄ and WF₆ or the like as producedduring etching process along with solid component impurities such asSiO₂ and WO₃ or else. SiF₄ that is contained in the exhaust gas isdecomposed into SiO₂ and HF by reaction of Equation (1) below.SiF₄+2H₂O

SiO₂+4HF  (1)

SiO₂ thus generated is ultra-fine or “micro” solid particles so that itis removed away from the exhaust gas by use of the sprayed water,simultaneously when it is produced. Other solid components (such as SiO,WO₃ and the like) that are contained in the exhaust gas when drained outof the etchers are also removed away. Regarding HF also, this issignificant in water solubility; thus, it is possible to remove it fromthe exhaust gas in a similar way. Water which contains SiO₂ withonce-removed HF being soluble thereinto drops down into theneutralization tank 61. WF₆ that is contained in the exhaust gas alsoreacts with water to thereby produce WO₃ (tungstic oxide) and HF in away as defined by Equation (2).WF₆+3H₂O

WO₃+6HF  (2)

WO₃ is ultrafine solid particles and thus is removed from the exhaustgas by the sprayed water and then drops down into the neutralizationtank 61 together with water. Silicon components and tungsten componentswhich are contained in the exhaust gas may be removed away by bubblingsuch exhaust gas into water in a water tank.

As has been described previously, the solid component removing device 54is operable to remove not only the solid components (SiO₂, WO₃ and thelike) contained in the exhaust gas being supplied thereto but alsoacidic gases (SiF₄ and WF₆ or else) which produce solid components byreaction with water. During removal of an acidic gas which purifies suchsolid components, the solid component removing device 54 also removesthe solid components (SiO₂, WO₃ and the like) thus generated by reactionwith water. Since these acidic gases are removed through reaction withwater within the solid component removing device 54 at a pre-stage ofthe reactor 11, it is possible to avoid unwanted production of solidcomponents (SiO₂, WO₃ and the like) within the reactor 11 by reactionbetween such acidic gases (SiF₄ and WF₆ or else) and reactive water assupplied to the space 14. Thus it is possible to solve the problems dueto production of solid components (SiO₂, WO₃ and the like) within thereactor 11—that is, (1) solid components badly behave to block porouscomponents as formed at a catalyst, and (2) solid components block gapsto be formed between the catalyst. Whereby the catalyst which comes intocontact with the exhaust gas does not decrease in surface area so thatthe PFC decomposition efficiency is improved.

The alkali water solution (e.g. sodium hydrate solution) within thealkali tank 39 is driven by the pump 42 to be supplied to theneutralization tank 61 through the pipe 43. The alkali solution acts toneutralize acidic materials such as HF or the like as contained in thewater within the neutralization tank 61. The neutralized water withinthe neutralization tank 61 is driven by the pump 36 and then drained outas waste water to the water drain pipe 37. Part of such waste water issent through the pipe 38 to the spray 63 and then sprayed thereby intothe interior of the solid component removing device 54. The remainingwaste water is drained out to waste water processing equipment as willbe later discussed in the description. As the reaction of Equations (1)and (2) takes place due to the water in the waste water being sprayedfrom the spray 63 also, it is possible to reduce the use amount of newwater to be sprayed from the spray 62. This results in a decrease inamount of the waste water being drained through the water drain pipe 37.The water as sprayed by the sprays 62, 63 absorbs acidic gases thatreside within the exhaust gas to be supplied to inside of the solidcomponent removing device 54 to thereby remove acidic gases away fromthe exhaust gas.

The exhaust gas which is drained out of the solid component removingdevice 54 is then introduced into the reaction unit 11 through the pipe26—practically, to the space 14 of the heating unit 12. Water (reactivewater) that is guided by the water supply pipe 35 is added to theexhaust gas within the space 14. In lieu of this water, water vapor orsteam may be added to the exhaust gas. The exhaust gas and the addedwater within the space 14 are heated up by the heater device 13 so thatthe water becomes a steam. The exhaust gas as heated up by the heatingunit 12 is then supplied through the duct 15 to the space 19 within thereaction unit 16. The exhaust gas is further heated up by the heaterdevice 18 within the space 19 up to a temperature which ranges from 650to 750° C. The heated exhaust gas flows into the inside of the catalystlayer 17. The catalyst layer 17 is filled with an alumina-based (Al₂O₃)catalyst—that is, a catalyst which has a composition of 80% of Al₂O₃ and20% of NiO₂. Practically, such alumina-based catalyst is installedwithin the reactor 16 while making up an exchangeable cartridge typestructure. CF₄ that is contained in the exhaust gas is decomposed intoHF and CO₂ while being accelerated in reaction with the reactive waterby the chemical reaction of the catalyst in a way as given by Equation(3).CF₄+2H₂O

CO₂+4HF  (3)

Upon decomposition of 1 mole of CF₄, 4 mole of hydrofluoric acid (HF) isproduced, which is four times greater in mount than the former. Notehere that in case the PFC contained in the exhaust gas is C₂F₆, reactionsuch as defined by Equation (4) occurs causing C₂F₆ to be decomposedinto CO₂ and HF.C₂F₆+3H₂O+(½)O₂

2CO₂+6HF  (4)

Oxygen for use during the reaction of Equation (4) is supplied as air tothe interior space 14 via an air supply pipe (not shown). This air isheated up within the spaces 14, 19 and is then supplied to the catalystlayer 17. Alternatively, in case SF₆ is used as the PFC, reactiondefined by Equation (5) takes place causing SF₆ to be decomposed intoSO₃ and HF.SF₆+3H₂O

SO₃+6HF  (5)

Upon decomposition of 1 mole of SF₆, 1 mole of SO₃ and 6 moles of HFwhich is six times greater in mount than it are produced.

The water that is guided by the water supply pipe 33 is sprayed by thespray 23 within the acidic gas removing device 22. This water iscollected by the acidic gas removing device 22 into the cooler device20. The water within the cooler device 20 is driven by the pump 29 sothat it is drained to the water drain pipe 30. A portion of this wateris supplied by the pipe 32 to the spray 21 whereas another portion of itis supplied by the pipe 31 to the spray 24; then, these are sprayed fromrespective ones.

In this embodiment, acidic substances such as HF and the like which areseparated from exhaust gases and resolved in water is neutralized bysupplying alkali solution to the neutralization tank 61 and the coolerdevice 20; thus, respective neutralization-processed waste water asdrained out of the neutralization tank 61 and cooler device 20 improvein absorption ability (solubility) of acidic gases such as HF and thelike as contained in the exhaust gases. Part of the waste water may bereused as the water to be sprayed from the corresponding sprays 63 and24 to thereby make it possible to enhance the efficiency of removal ofacidic gases contained in the exhaust gases.

The interior of an entire system including the pre-processing tower 10,the reactor 11, the cooler device 20 and acidic gas removing device 22is retained by the blower 25 at negative pressures to thereby preventleakage of HF or the like contained in the exhaust gas toward theoutside of this system. Additionally the acidic gas removing device 22is also modifiable to employ the bubbling scheme. Note however thateither the spray scheme or the filling tower scheme is superior becauseof its advantage as to reduced pressure losses and the capability todownsize the blower for gas exhaust use.

The alkali water solution within the alkali tank 39 is driven by thepump 40 so that it is supplied through a pipe 41 to the interior of thecooler device 20. The alkali solution is used within the cooler device20 to neutralize specific acidic substances such as HF and the likewhich are contained in the water drained out of the acidic gas removingdevice 22 and the water as sprayed from the spray 21, respectively. Theneutralized water within the cooler device 20 is driven by the pump 29and then drained through the water drain pipe 30 to waste-watertreatment equipment (not shown). The wastewater treatment equipment isfor removal of fluorine (also including fluorine contained as fluorides)as contained in waste water being supplied by the water drain pipes 30,37 and also for outward delivery of the waste water from which fluorinewas removed away.

The illustrative embodiment is such that all of the semiconductorfabrication apparatuses (etchers and chemical vapor deposition (CVD)equipment) which are installed within the clean room and to which PFCgases are supplied are connected via the duct 7 to the PFC decompositiondevice 9. With such an arrangement, it is possible to permit a singlemachine of PFC decomposition device 9 to process the PFC gases drainedout of all of them in a concentrated way. Unlike the prior art, thisembodiment is free from the need to connect a water supply pipe and awater drain pipe plus electrical wiring leads to a respective one of theplurality of PFC decomposition devices which are installed within theclean room and may be arranged so that such water supply and drain pipesand electrical wiring leads are connected to the single machine of PFCdecomposition device 9. This in turn makes it possible to shorten a timetaken to install the water supply/drain pipes and electrical wiringleads while at the same time reducing difficulties in installation worksthereof.

In this embodiment the PFC decomposition device 9 is installed outsideof the clean room 2. Due to this, in case a clean room is newlyinstalled, the embodiment avoids a need to provide in the clean room 2an extra installation space for the PFC decomposition device 9 and thewater supply/drain pipes to be connected thereto, thereby enablingachievement of likewise size reduction or “downsizing” of the clean room2. Another advantage lies in an ability to reduce the capacity ofcleaning equipment for removal of residual contaminants or micro-dustswithin the clean room 2 and that of air-conditioning/adjustmentequipment which is operatively associated with the clean room 2. Afurther advantage lies in an ability to make easier both downsizing ofthe clean room 2 and layout alteration of semiconductor fabricationapparatuses. This can be said because the PFC decomposition device 9 andany required water supply/drain pipes connected thereto are not disposedwithin the clean room 2.

In cases where a PFC decomposition device is newly installed forprocessing of PFC gases as drained out of a plurality of etchersinstalled within the currently established clean room, installing thePFC decomposition device 9 outside of the clean room 2 in the way ofthis embodiment makes it easier to move the semiconductor fabricationapparatuses such as the etchers and replace such semiconductorfabrication apparatuses in accordance with a change of products to bemanufactured. To be brief, this embodiment is capable of achieving aflexibility-increased semiconductor factory through alteration andrecombination of flexible production lines. It is also possible tonoticeably shorten or eliminate a time taken to move the semiconductorfabrication apparatuses. In addition, it is possible for this embodimentto introduce the PFC decomposition device 9 by merely installing theduct 7 within the clean room 2, without requiring movement of suchsemiconductor fabrication apparatuses. For this reason, uponintroduction of the PFC decomposition device 9, it becomes possible toshorten a halt/shut-down time period of the semiconductor fabricationapparatus otherwise occurring due to the semiconductor production lineswithin such clean room 2.

This embodiment is such that the reactor 11 is subdivided into theheating unit 12 and the reaction unit 16 each having its own heaterdevice, with the heating unit 12 and the reaction unit 16 installed onthe indoor floor of a little house. This arrangement for division of thereactor 11 into two parts of the heating unit 12 and reaction unit 16 isemployed because in view of the concentrated processing of PFC gases asdrained out of all the semiconductor fabrication apparatuses which areinstalled within the clean room 2 and to which PFC gases are supplied,the total height of reactor 11 (i.e. the height of heating unit 12 andthat of reaction unit 16) becomes extremely significant to an extentthat which makes it difficult to transport them by land vehicles.

This embodiment merely requires connection between the gas exhaustportion of an etcher to be additionally provided and the duct 7; thus,it is possible to readily perform additional installation of any extraetcher within the clean room 2. A PFC gas to be drained out of the addedetcher may be processed by the PFC decomposition device 9 which isinstalled outside of the clean room 2. Note here that the embodiment isarranged to remove any acidic gas (or carbon monoxide) as drained out ofan etcher by the acid gas removing device 4 (or carbon monoxide removaldevice 6) that is installed at a location adjacent to the outlet or“exit” port of the etcher; thus, it is possible to preclude damages ofworking environment within the clean room 2 even where the duct 7 isdamaged within the clean room 2. Additionally, improving the reliabilityof the duct 7 enables installation of harmful gas processing equipmentfor treatment of these harmful gases (carbon monoxide, chlorine andothers) at a location outside of the clean room 2 and also in theupstream of the PFC decomposition device 9 to thereby achieveconcentrated processing of these harmful gases.

An explanation will be given of another embodiment of the PFCdecomposition device with reference to FIG. 3 below. A PFC decompositiondevice 9A of this embodiment is arranged so that a water vaporizer 55 isinstalled at the pipe 27 of the PFC decomposition device 9A, with thewater supply pipe 35 being connected to the water vaporizer 55 and witha steam supply pipe 56 provided to couple together the water vaporizer55 and the space 14 of the heating unit 12. The remaining arrangement ofthe PFC decomposition device 9A is the same as that of the PFCdecomposition device 9 stated supra. Within the water vaporizer 55, ahigh-temperature exhaust gas to be supplied by the pipe 27 flows in aheat transfer pipe (not shown) whereas water (reactive water) beingsupplied by the water supply pipe 35 flows on the shell side. Water isheated up by the exhaust gas within the water vaporizer 55 to therebybecome a steam. The steam thus generated is supplied through the steamsupply pipe 56 to the space 14 and is then added to the exhaust gas.

In cases where the PFC decomposition device 9 which performsconcentrated processing of PFC gases as drained out of all the etcherswithin the clean room 2 interrupts its PFC gas treatment operation dueto malfunction or the like, semiconductor fabrication processes withinsuch clean room 2 are all halted. In this embodiment, in emergencyevents in which the PFC decomposition device 9 stops, let the three-wayvalve 8 rotate to thereby provide connection between the duct 7 on theupstream side of the three-way valve 8 and the pipe 60. The exhaust gaswhich was drained out of each etcher is driven by the blower 50 to betemporarily introduced into the acidic gas removing device 47 throughthe pipe 60 and gas collection duct 49, rather than to the PFCdecomposition device 9. Acidic gases that reside in such exhaust gaswill be removed by the acidic gas removing device 47. Generally the gasprocessing capacity of the acidic gas removing device 47 is about ten tofifty times greater than the capacity of exhaust gas being supplied bythe duct 7 to the PFC decomposition device 9. Due to this, it ispossible for the acidic gas removing device 47 to remove the acidicgases residing in the exhaust gas being supplied to the PFCdecomposition device 9. The resulting exhaust gas from which the acidicgases are removed is drained out of the exhaust gas cylinder 52 toexternal environment. During introduction of such exhaust gas via thepipe 60 to the acidic gas removing device 47, the required operationcheck and repair of the PFC decomposition device 9 which ismalfunctioning are carried out. After completion of repairing tasks,rotate the three-way valve 8 to supply the exhaust gas to the PFCdecomposition device 9. In this way, this embodiment is capable ofsupplying the exhaust gas via the pipe 60 to the acidic gas removingdevice 47 in emergency events such as malfunction or the like of the PFCdecomposition device 9 whereby it becomes possible to perform operationcheck and repair works without requiring interruption of thesemiconductor fabrication processes within the clean room 2. As a timeperiod required for operation check and repair of the PFC decompositiondevice 9 is about one to two days, the amount of a PFC gas which isreleased to external environment without being decomposed stays at anextremely small rate with respect to the PFC gas amount to be yearlyprocessed by the PFC decomposition device 9 in this embodiment.

This embodiment is also capable of using the PFC decomposition device 9to process a PFC gas which is drained out of the CVD apparatus asinstalled in the clean room 2.

In case a machine room for installation of air purification apparatusfor purifying indoor air of the clean room 2 and air-conditioningequipment of clean room 2 is provided inside of the machine-roomsemiconductor fabrication factory 1 or alternatively within a buildingassociated with the semiconductor fabrication factory, the PFCdecomposition device 9 may be installed within such machine room. ThePFC decomposition device 9 in which the reactor 11 is divided into theheating unit 12 and reaction unit 16 does not require any reconstructionfor making the ceiling of such machine room higher and thus is readilyinstallable in the machine room.

It is also permissible to avoid installation of the three-way valve 8and pipe 60 and instead install PFC decomposition devices 9 in parallelto the duct 7 while causing these PFC decomposition devices 9 to offerswitchable operability. With such an arrangement, even if one PFCdecomposition device 9 malfunctions then the other PFC decompositiondevice 9 is employable to perform exhaust gas processing (removal ofresidual acidic gases and PFC decomposition treatment). Additionally,the operation check and repair of a malfunctioning PFC decompositiondevice 9 may be done while continuously performing semiconductorfabrication processes.

The PFC decomposition device 9C is equipped with a reactor 11, filerdevices 65, 66 and fine-particle/powder silo 81. The duct 7 is coupledto a lower-part space 68 of the filter device 65. The pipe 26 which iscoupled to the heating unit 12 is coupled to an upper-part space of thefilter device 65. The pipe 27 is coupled to a lower space 68 of thefilter device 66. The exhaust gas duct 28 is coupled to an upper space69 of the filter device 66. The powder silo 81 is connected by a pipe 82to the duct 7 at a location in the downstream of the three-way valve 8and also connected by a pipe 83 to the pipe 27, respectively.

The PFC decomposition device 9A offers the same function as the PFCdecomposition device 9 and can obtain the same effects and advantages asthe latter. Since the PFC decomposition device 9A is designed to use theheat of an exhaust gas drained out of the reaction unit 16 to change thereactive water into a steam, it is possible to reduce the thermal energybeing applied for heat-up of the exhaust gas at the heating unit 12 ofthe PFC decomposition device 9A. This is because no energies arerequired to change the reactive water into a steam in the PFCdecomposition device 9.

Even where the PFC decomposition device 9A is used in place of the PFCdecomposition device 9 in the PFC processing apparatus 44 shown in FIG.1, it is possible to obtain similar effects occurring in the PFCprocessing apparatus 44 of Embodiment 1.

An explanation will be given of another embodiment of the PFCdecomposition device with reference to FIG. 4 below. A PFC decompositiondevice 9B of this embodiment is arranged so that a gas pre-heater 57 isinstalled at the pipe 26 of the PFC decomposition device 9 with the pipe26 connected via this gas preheater 57 to the space of the heating unit12. The other arrangement of the PFC decomposition device 9B is the sameas that of the PFC decomposition device 9. A high-temperature gas whichis drained out of the catalyst layer 17 and supplied by the pipe 27flows in a heat-transfer pipe (not shown) as provided within the gaspreheater 57 whereas an exhaust or waste gas being supplied via the pipe26 flows on the shell side within the gas preheater 57. The exhaust gasbeing supplied by the pipe 26 is heated up by the high-temperatureexhaust gas as supplied by the pipe 27 and then introduced into thespace 14 in the state that its temperature rose up. The high-temperatureexhaust gas flowing in the heat transfer pipe that is provided withinthe gas preheater 57 is introduced into the cooler device 20 and thencooled down in the way stated previously.

The PFC decomposition device 9B offers the same function as the PFCdecomposition device 9 and can obtain the same effects and advantages asthe latter. Since the PFC decomposition device 9B is arranged to use theheat of an exhaust gas as drained out of the reaction unit 16 to heat upthe exhaust gas being supplied to the heating unit 12, it is possible toreduce the thermal energy being applied for heat-up of the waste gas atthe heating unit 12 of the PFC decomposition device 9B.

Even where the PFC decomposition device 9B is used in lieu of the PFCdecomposition device 9 in the PFC processing apparatus 44 shown in FIG.1, similar effects occurring in the PFC processing apparatus 44 ofEmbodiment 1 are obtainable.

Embodiment 2

A PFC processing apparatus in accordance with another embodiment of thepresent invention will be explained with reference to FIG. 5. The PFCprocessing apparatus 44A of this embodiment is arranged so that theexhaust duct 28 is connected to the acidic gas removing device 47 in thePFC processing apparatus 44 shown in FIG. 1. An arrangement of the otherpart of PFC processing apparatus 44A is the same as that of the PFCprocessing apparatus 44. In this embodiment, an exhaust gas which wasdrained out of the acidic gas removing device 22 of the PFCdecomposition device 9 is supplied through the exhaust gas duct 28 tothe acidic gas removing device 47. Due to this, in case the acidic gasremoving device 22 decreases in acidic gas removal functionality, anyacidic gas to be produced by PFC decomposition within the reaction unit16 can be removed by the acidic gas removing device 47. In this way, itis possible to use the acidic gas removing device 47 as a backup of theacidic gas removing device 22. The PFC processing apparatus 44A of thisembodiment can also obtain the effects occurring at the above-stated PFCprocessing apparatus 44.

In the PFC processing apparatus 44A of this embodiment, the acidic gasremoving device 22 of the PFC decomposition device 9 may be deleted toremove the acidic gas as produced by PFC decomposition within thereaction unit 16 not by the acidic gas removing device 22 but by theacidic gas removing device 47. In this case the acidic gas removingdevice 47 is designed to operate continuously during semiconductormanufacturing. In the PFC processing apparatus 44A, it is also possibleto replace the PFC decomposition device 9 with either one of the PFCdecomposition device 9A and the PFC decomposition device 9B.

Embodiment 3

A PFC processing apparatus in accordance with still another embodimentof the present invention will be explained below. The PFC processingapparatus 44B of this embodiment is arranged so that the PFCdecomposition device 9 in the PFC processing apparatus 44 shown in FIG.1 is replaced by a PFC decomposition device 9C shown in FIG. 6. Theother arrangement of the PFC processing apparatus 44B is the same asthat of the PFC processing apparatus 44. An arrangement of the PFCdecomposition device 9C that is used in the PFC processing apparatus 44Bwill be explained. Whereas the PFC decomposition device 9 is a wet-typePFC decomposition device in which waste water generates the PFCdecomposition device 9C used in this embodiment is a dry-type PFCdecomposition device in which no waste water generates.

The high-temperature exhaust gas which was drained out of the catalystlayer 17 and which contains CO₂ and HF as decomposed gases is introducedinto the cooler device 20. This high-temperature exhaust gas is thencooled down by the water being continuously sprayed from the spray 21within the cooler device 20 to a temperature less than or equal to100.degree. C. A portion of HF as produced by decomposition of CF₄ isresolved into the sprayed water and then removed away. Cooling of theexhaust gas may alternatively be carried out by bubbling the exhaust gasinto water within a water tank. The temperature-decreased exhaust gas isintroduced into the acidic gas removing device 22. The exhaust gas comesinto contact with the water being sprayed from the sprays 23, 24 withinthe acidic gas removing device 22. Whereby, the acidic gas (produced bydecomposition of PFC) such as HF contained in the exhaust gas is solvedinto such water and thus is removed away from the exhaust gas. In orderto enhance the contact efficiency between the exhaust gas and the waterwhile at the same time improving the efficiency of acidic gas removal,plastic-made cylindrical piece is filled within the acidic gas removingdevice 22. HF is reduced in amount by the acidic gas removing device 22to fall within a range of from several % to 1 ppm or less. The resultantharmless exhaust gas is then drained away through the driving blower 25and exhaust duct 28 plus exhaust gas cylinder 52 toward the externalenvironment. In addition, the water that has absorbed acidic gases isdrained by the acidic gas removing device 22 into the cooler device 20.

An arrangement of the filter device 65, 66 will be explained withreference to FIG. 7. The filter device 65, 66 includes a plurality oftubular filter elements 67A, 67B, 67C or the like which are installedwithin a vessel-like housing 80. Each filter element has a filter fabricor cloth (not shown) which is wound around an outer surface. An insidespace of the vessel 80 is subdivided by each filter element into thelower space 68 and upper space 69. An air supply pipe 70A with a valve71A provided therein is inserted from the upper part into the inside offilter element 67A. Similarly, an air supply pipe 70B with a valve 71Bprovided therein is inserted from the upper part into the inside offilter element 67B; an air supply pipe 70C with a valve 71C providedtherein is inserted from the upper part into the inside of filterelement 67C. A solid component reservoir tank 72 is connected throughthe valve 77A to a bottom portion of the vessel 80 of the filter device65. A screw conveyer 74 is disposed beneath the solid componentreservoir tank 72. A solid component reservoir tank 73 is connected viathe valve 77B to the bottom of the vessel 80 of the filter device 66. Ascrew conveyer 75 is laid out below the solid component reservoir tank73.

As has been described in Embodiment 1, the exhaust gas being guided bythe duct 7 contains several impurities along with PFC (CF₄), examples ofwhich are an impurity that produces solid components by reaction withwater such as SiF₄ and WF₆ as produced during etching processes and animpurity that is a solid component such as SiO₂ and WO₃ or else. Thisexhaust gas is supplied into the lower space 68 of the filter device 65.Power particles of Ca salts as filled within the powder silo81—typically, powder of calcium hydroxide [Ca(OH)₂]—is supplied throughthe pipe 82 to the duct 7 when a valve (not shown) opens. The powderCa(OH)₂ is mixed into the exhaust gas and then flows into the lowerspace 68 of the filter device 65. SiF₄ and WF₆ contained in the exhaustgas experience neutralization reaction with Ca(OH)₂ as indicated inEquations (6) and (7) to thereby produce CaF₂, SiO₂ and WO₃.2Ca(OH)₂+SiF₄

2CaF₂+SiO₂+2H₂O  (6)3Ca(OH)₂+WF₆

3CaF₂+WO₃+3H₂O  (7)

Further, HF contained in such exhaust gas experiences chemical reactionwith Ca(OH)₂ indicated by Equation (8) below to thereby produce calciumfluoride (CaF₂). Solid components such as SiO₂ and WO₃ contained in theexhaust gas and unreacted Ca(OH)₂ along with CaF₂, SiO₂ and WO₃ asproduced by the reaction of Equations (6), (7) and (8) are trapped bythe filter cloth installed in each filter element 67 of the filterdevice 65 and are then removed away from the exhaust gas. The exhaustgas which has passed through the filter element 67 and contains CF₄flows into the spaces 14, 19 within the reactor 11 through the upperspace 69 and pipe 26. CF₄ is decomposed by the catalyst layer 17 in theway stated previously in Embodiment 1. The exhaust gas being supplied tothe reactor 11 contains none of HF, SiF₄, WF₆, SiO₂ and WO₃.

The acidic gas (HF) that was produced by decomposition of CF₄ at thecatalyst layer 17 is introduced into the space 68 of the filter device66. Opening a valve (not shown) permits Ca(OH)₂ power within the powdersilo 81 to be supplied by the pipe 83 to the pipe 27 and then mixed intothe exhaust gas. Ca(OH)₂ also is introduced into the space 68. HFexperiences occurrence of neutralizing reaction with Ca(OH)₂ as given byEquation (8) to thereby produce CaF₂.Ca(OH)₂+2HF

CaF₂+2H₂O  (8)

This CaF₂ and unreacted Ca(OH)₂ are captured by the filter cloth withinthe filter device 66. During penetration of a layer of CaF₂ andunreacted Ca(OH)₂ and CaF₂ which was formed as a result of capture atsurfaces of the filter cloth, unreacted HF reacts with such Ca(OH)₂ andis then fixed. Chemical reaction between HF and Ca(OH)₂ is acceleratedat higher temperatures. As the exhaust gas drained out of the catalystlayer 17 is high in temperature, its chemical reaction is accelerated.Coolant air is supplied by a pipe 76 to the upstream side of the filterelement 67 of the filter device 66, that is, into the lower space 68.This coolant air is used to cool the exhaust gas within the lower space68 whereby the temperature of such exhaust gas is adjusted so that it isgreater than or equal to about 200° C. and yet below 300° C. This isbecause the heat-resistance temperature of filter cloth is 300° C.Preferably the supply position of coolant air is in the downstream of ajunction point of the pipe 27 and pipe 83. This is required because HFand Ca(OH)₂ powder are mixed and contacted together at highertemperatures to thereby efficiently execute the neutralization reaction.Under the high temperature condition, Ca(OH)₂ becomes CaO and then theactivity as the alkali lowers. In this embodiment, in the upstream sidesince the reaction water is added to use the perfluoride decomposingreaction, many water components is existed, even under the hightemperature condition, Ca(OH)₂ exists. For this reason, since thereaction shown in the formula (8) is the high temperature condition, thereaction speed is accelerated, and then HF is removed effectively. Asthe blower 25 is driving, the exhaust gas is drained from the filterdevice 66 to the exhaust duct 28. The exhaust gas being drained to theexhaust duct 28 contains no acidic gases. The exhaust gas within theexhaust duct 28 is cooled by the coolant air which is supplied from thepipe 84 into the exhaust duct 28 and thus drops down at 50° C. Due tosupplement of the air which decreases to 50° C., it will no longerhappen that H₂O generated by the reaction of Equation (8) is condensedto change into a liquid.

At the filter devices 65, 66, a difference in pressure between the upperspace 69 and lower space 68 is detected by a differential pressure meteror gauge (not shown). At a filter device in which such pressuredifference reaches a preset value, e.g. filter device 66, its filterelements are subjected to back washing. More specifically, the firststep is to open the valve 71A. Backwash-use water which is supplied fromthe air supply pipe 70A is drained to the inside of filter element 67Aand then passes through the filter cloth and thereafter is drained tothe lower space 68. Due to the flow of this backwash-use water, solidcomponents (such as calcium fluoride, unreacted Ca(OH)₂ and the like)which are attached to outer surfaces of the filter cloth drop down as abalk onto the bottom of the vessel 80. After having completed the backwashing of the filter element 67A, the valve 70C is driven to open sothat air is supplied from the air supply pipe 70B to the filter element67B to thereby perform back washing of the filter element 67B. Next, theair being supplied from the air supply pipe 70B is used to perform backwashing of the filter element 67C. By opening the valve 77B, solidcomponents 79 that are accumulated at the bottom of the vessel 80 aredrained to the interior of solid component reservoir tank 73. Further,the solid components 79 which have dropped down through the opened valve78B are transferred by the screw conveyer 75 toward a solid mattercollection silo (not shown) and then stored therein. Each filter elementof the filter device 65 is subject to back washing in a similar way,causing the solid components 79 within the vessel 80 to be drained intothe solid component reservoir tank 72 when letting the valve 77A open.Such solid components also drop down through the valve 78A and are thensent by the screw conveyer 74 to the above-noted solid matter reservoirtank. The solid components 79 within the solid matter reservoir tank arefor later reuse as the raw material of cement.

Another example of the Ca salt useable in place of Ca(OH)₂ is powder ofcalcium carbonate (CaCO₃) or calcium oxide (CaO). Regarding reactivitywith acidic gases or the like, Ca(OH)₂ is higher than CaCO₃ and CaO;thus, it is preferable to use Ca(OH)₂. Reaction with acidic gases orelse takes place on surfaces; thus, in order to increase the surfacearea, it is preferable that Ca salt is in the form of powder. In caseCaCO₃ is added to the exhaust gas within the duct 7, neutralizationreaction with SiF₄ and WF₆ as defined by Equations (9) and (10) takesplace.2CaCO₃+SiF₄

2CaF₂+SiO₂+2CO₂  (9)3CaCO₃+WF₆

3CaF₂+WO₃+3CO₂  (10)

In case CaO is added to the exhaust gas within the duct 7,neutralization reaction with SiF₄ and WF₆ as given by Equations (11) and(12) occurs.2CaO+SiF₄

2CaF₂+SiO₂  (11)3CaO+WF₆

3CaF₂+WO₃  (12)

CaF₂, SiO₂ and WO₃ or else as produced through each reaction of them areremoved away by the filter cloth of the filter device 65.

In case CaCO₃ is added to the exhaust gas within the pipe 27,neutralization reaction with HF as represented by Equation (13) occurs.CaCO₃+2HF

CaF₂+H₂O+CO₂  (13)

In case CaO is added to the waste gas within the pipe 27, neutralizationreaction with HF as given by Equation (14) occurs.CaO+2HF

CaF₂+H₂O  (14)

CaF₂ or else which was produced by each reaction of them is removed bythe filter cloth of filter device 66.

In Embodiments 1 and 2 using the wet-type PFC decomposition devices, itis required to remove fluorides that are contained in the waste water asguided by the water drain pipes 30, 37 in waste-water processingequipment. Due to this, in the wastewater processing equipment, thefollowing processing is done. More specifically, add Ca salt (CaCO₃ orCa(OH)₂) into waste water; then, stir it. Solid components such ascalcium fluoride produced by reaction between Ca salts and HF beingcontained in the waste water and unreacted Ca salts and othersprecipitate for separation. Further, add a flocculent to the wastewater, causing such solid components with micro-particle diameters toaggregate or flocculate for separation. The resultant solid componentsthus separated such as calcium fluorides are subject to dehydration anddrying processes for later reuse as the raw material of cement.Embodiments 1 and 2 which use water to remove solid components andacidic gases in the exhaust gas should require execution of theabove-stated complicated processing for removal of fluorides ascontained in the waste water, resulting in production of a great amountof water. The waste water from the wastewater processing equipmentcontains therein an increased amount of calcium ions and is drainedexternally as industrial waste water. Although Embodiments 1 and 2 arecapable of obtaining various effects stated above, these requirewastewater processing facilities which perform complicated processingfor fluoride removal.

In contrast, this embodiment is arranged to add Ca salt to the exhaustgas whereby it is possible to salvage fluorides in the exhaust gas as areusable solid content without producing any waste water. Obviously,this embodiment requires no wastewater processing facilities. Installingthe PFC processing apparatus of this embodiment which is extremely lessin water use amount makes it possible to install a semiconductorfabrication factory in land areas with poor water resources. Inaddition, even if the environmental emission standards become stricterin near future, the embodiment may readily cope with such strictness. Asthe embodiment is free from a risk of waste water production, any waterdrain pipes are no longer required; thus, it is possible to simplify thefacilities when compared to Embodiments 1 and 2 stated supra. Generally,chemical reaction in the dry state is slower in reaction rate and lessin efficiency than chemical reaction in an ionized state in wet-typeones. However, wet-type PFC decomposition devices inherently requireaddition of an access amount of calcium salt (Ca(OH)₂, CaCO₃, CaO orelse) which is several times greater than a theoretically determinedvalue in order to remove a low concentration of F ions in waste water sothat the requisite amount of Ca salt is nearly equal to that of thewet-type PFC decomposition devices.

In case SF₆ is used as the PFC gas in an etcher(s), SO₃ is produced byreaction of Equation (5) at the catalyst layer 17. This SO₃ reacts withthe Ca salt added to the interior of pipe 27, resulting in production ofcalcium sulfate (CaSO₄). Practically explaining, in case any one ofCa(OH)₂, CaCO₃ and CaO is added, reaction represented by any one ofEquations (15) to (17) occurs.Ca(OH)₂+SO₃

CaSO₄+H₂O  (15)CaCO₃+SO₃

CaSO₄+CO₂  (16)CaO+SO₃

CaSO₄  (17)

This calcium sulfate is later reusable as the raw material of cement.

This embodiment can obtain the effects and advantages occurring inEmbodiment 1, including (1) the ability to downsize the clean room 2 andto readily perform layout changes of the semiconductor fabricationapparatuses, (2) easing transfer of semiconductor fabricationapparatuses such as etchers or the like within the currently establishedclean room and replacement of any semiconductor fabrication apparatus,(3) capability to shorten the interruption time period of semiconductormanufacture using semiconductor fabrication lines within the clean room2 upon introduction of the PFC decomposition device 9, (4) achievingenhanced transportability by land vehicles because of subdivision of theheating unit 12 and reaction unit 16, (5) ability to readily performadditional installation of etchers within the clean room 2 because whatis required is to merely connect together the gas exhaust part of anetcher to be additionally provided and the duct 7, and (6) improvementin catalyst-based PFC decomposition efficiency due to the fact that nosolid components are produced through reaction with reactive water.

In the PFC decomposition device 9C of FIG. 6, slurry of Ca salt (CaCO₃or Ca(OH)₂) may be supplied to the pipe 27 in lieu of supplement of Casalt powder. The Ca salt is such that slurry is more readilytransportable than powder, thereby facilitating supplement to the pipe27. Water component of the Ca salt slurry is vaporized into a steam whencoming into contact with a high-temperature exhaust gas being drainedout of the reaction unit 16. An acidic gas (HF) in the exhaust gasreacts with Ca salt to produce calcium fluorides. The steam is guided topass through the filter cloth and then release toward externalenvironment through the exhaust duct 28 and exhaust cylinder 52. Thisembodiment is arranged to supply coolant water from the pipe 84 tothereby ensure that an exhaust gas temperature within the exhaust duct28 stays at 100° C. Thus it is possible to avoid unwanted flocculationof the steam within the exhaust duct 28.

The PFC decomposition device 9C of this embodiment is also applicable toPFC processing apparatus with its associated PFC decomposition deviceinstalled within the clean room 2.

Other embodiments of the dry-type PFC decomposition device will beexplained. A PFC decomposition device 9D (see FIG. 8) is arranged sothat a water vaporizer 55 is installed at the pipe 27 in a similar wayto that of the PFC decomposition device 9A while heating up the reactivewater to be supplied by a water supply pipe 35. A PFC decompositiondevice 9E shown in FIG. 9 is designed so that a gas preheater 57 isinstalled at the pipe 27 for heating an exhaust gas being guided by apipe 26. A respective one of the PFC decomposition devices 9D and 9E maybe installed in the PFC processing apparatus 44B in place of the PFCdecomposition device 9C of Embodiment 3. Further in the PFC processingapparatus 44A also, each of the PFC decomposition devices 9D and 9E isinstallable in lieu of the PFC decomposition device 9.

In a liquid crystal manufacturing system including a liquid crystalmanufacturing factory also, more than one etcher (or CVD apparatus)using PFC gases is installed within a clean room as liquid crystalmanufacturing equipment. Due to this, applying any one of theabove-stated PFC decomposition devices 44, 44A and 44B to the liquidcrystal manufacturing system makes it possible to concentratedly processPFC gases as drained out of all the etchers within the clean room. ThePFC decomposition device (any one of the PFC decomposition devices 9,9A, 9B, 9C, 9D and 9E) of such PFC processing apparatus is installedoutside of the clean room in a similar way to Embodiments 1 and 2.

Although the PFC processing apparatus of each of the embodiments statedsupra employs the catalyst-use PFC decomposition device as its PFCdecomposition device, this PFC decomposition device is replaceable by acombustion-scheme PFC decomposition device for performing decompositionthrough combustion or alternatively a plasma-scheme PFC decompositiondevice for decomposition by changing PFC into a plasma. Additionally theblower 25 is replaceable with an ejector(s). Each of the above-statedembodiments is capable of decomposing PFCs including but not limited toCF₄, CHF₃, C₂F₆, C₃F₈, C₄F₆, C₅F₈, NF₃, and SF₆.

According to the present invention, it is possible to downsize a cleanroom with either semiconductor fabrication apparatus or liquid crystalmanufacturing apparatus installed therein. In case the invention isapplied to the currently established clean room, it is no longerrequired to move the semiconductor fabrication apparatus or liquidcrystal manufacturing apparatus within the clean room in order toinstall more than one perfluoride decomposition device.

1. A perfluoride processing apparatus comprising: a perfluoridedecomposition unit comprising a heater adapted to heat aperfluoride-containing exhaust gas and a catalytic layer containing acatalyst for decomposing said perfluoride to an acidic substance; anacidic substance removing unit for removing said acidic substancecontained in an exhaust gas discharged from said perfluoridedecomposition unit, with Ca salts; and a Ca salt supply unit forsupplying said Ca salts in solid form to said acidic substance removingunit; whereby said perfluoride decomposition forms a dry-typeperfluoride decomposition unit in which no waste water generates.
 2. Aperfluoride processing apparatus comprising: a perfluoride decompositionunit comprising a heater adapted to heat a perfluoride-containingexhaust gas and a catalytic layer containing a catalyst for decomposingsaid perfluoride to an acidic substance; and an acidic substanceremoving unit for removing said acidic substance contained in an exhaustgas discharged from said perfluoride decomposition unit with Ca salts;wherein said perfluoride processing apparatus comprises further: areactive product substance removing unit for removing a solid reactionproduct of a substance contained in a perfluoride-containing gas withwater, and with Ca salts; whereby an exhaust gas discharged from saidreactive product substance removing unit is supplied to said perfluoridedecomposition unit.
 3. A perfluoride processing apparatus according toclaim 1, wherein: said heater having a first heater device beingsupplied said perfluoride-containing exhaust gas and a second heaterdevice being supplied said perfluoride-containing exhaust gas; saidcatalytic layer is filled with said catalyst; and said perfluorideprocessing apparatus comprises a reaction unit to which saidperfluoride-containing exhaust gas being heated by said first and secondheating devices is supplied.
 4. A perfluoride processing apparatusaccording to claim 1, wherein: said acidic substance removing unit has avessel and a filter element; said filter element is provided in saidvessel for removing said acidic substance and for passing through saidexhaust gas from which said acidic substance has been removed; a firstpiping communicating said exhaust gas being discharged from saidperfluoride decomposition unit to a first space which exists at anupstream side of said filter element provided in said vessel; and an Casalt supplying unit connected to said first piping and for supplyingsaid Ca salts to said exhaust gas being discharged from said perfluoridedecomposition unit which flows into said first piping.
 5. A perfluorideprocessing apparatus according to claim 4, wherein said perfluorideprocessing apparatus comprises further: a first reactive productreservoir unit provided at a lower portion of said acidic substanceremoving unit and communicated to said first space and for reservingsaid removed first reactive product; and a first transportation unit fortransporting acidic substance in said first reactive product reservoirunit.
 6. A perfluoride processing apparatus comprising: a perfluoridedecomposition unit comprising a heater adapted to heat aperfluoride-containing exhaust gas and a catalytic layer containing acatalyst for decomposing said perfluoride to an acidic substance; anacidic substance removing unit for removing said acidic substancecontained in an exhaust gas discharged from said perfluoridedecomposition unit, with Ca salts; wherein: said acidic substanceremoving unit has a vessel and a filter element; said filter element isprovided in said vessel for removing said acidic substance and forpassing through an exhaust gas from which said acidic substance has beenremoved; a first piping for communicating said exhaust gas beingdischarged from said perfluoride decomposition unit to a first space,which exists at an upstream side of said filter element provided in saidvessel; and a Ca salt supplying unit for supplying said Ca salts to saidexhaust gas which flows into said first piping, and, wherein saidperfluoride processing apparatus comprises further: an air supply pipefor introducing a back washing use air into said acidic substance, whichremoves said acidic substance being adhered to said filter element, to asecond space which exists at a downstream side of said filter elementprovided in said vessel.
 7. A perfluoride processing apparatus accordingto claim 2, wherein said perfluoride processing apparatus comprisesfurther Ca salt supplying unit for supplying said Ca salts to saidacidic substance removing unit.
 8. A perfluoride processing apparatusaccording to claim 3, wherein: said acidic substance removing unit has avessel and a filter element; said filter element is provided in saidvessel and for removing said acidic substance and for passing throughsaid exhaust gas from which said acidic substance has been removed; afirst piping for communicating said exhaust gas which contains saidsubstance for producing said solid component by a reaction with water toa first space which exists at an upstream side of said filter elementbeing provided in said vessel; a Ca salt supplying unit for supplyingsaid Ca salts to said exhaust gas which flows into said first piping;and a second piping for introducing said exhaust gas which has passedthrough said filter element, to said perfluoride decomposition unit. 9.A perfluoride processing apparatus according to claim 8, wherein saidperfluoride processing apparatus comprises further: a second reactiveproduct reservoir unit provided at a lower portion of said acidicsubstance removing unit and communicated to said first space and forreserving said removed second reactive product; and a firsttransportation unit for transporting said reactive product in saidsecond reactive product reservoir unit.
 10. A perfluoride processingapparatus according to claim 8, wherein said perfluoride processingapparatus comprises further: an air supplying pipe for introducing aback washing use air into said acidic substance, which removes saidacidic substance being adhered to said filter element, to said firstspace which exists at an upstream side of said filter element providedin said vessel.
 11. A perfluoride processing apparatus according toclaim 1, wherein said Ca salts are one selected from Ca(OH)₂, CaCO₃ andCaO.
 12. A perfluoride processing apparatus according to claim 2,wherein said heater having a first heater device being supplied saidperfluoride-containing exhaust gas and a second heater device beingsupplied said perfluoride-containing exhaust gas; and said perfluorideprocessing apparatus comprises further a reaction unit to which saidexhaust gas being heated by said first and second heating devices issupplied.
 13. A perfluoride processing apparatus according to claim 2,wherein said Ca salts are one selected from Ca(OH)₂, CaCO₃ and CaO. 14.A perfluoride processing apparatus comprising: a perfluoridedecomposition unit comprising a heater adapted to heat aperfluoride-containing exhaust gas and a catalytic layer filled with acatalyst for decomposing said perfluoride to an acidic substance; aheated exhaust gas containing said perfluoride and acidic substancesupply to said perfluoride decomposition unit; an acidic substanceremoving unit for removing said acidic substance contained in exhaustgas discharged from said perfluoride decomposition unit; and a reactiveproduct substance removing unit for removing a reactive productsubstance for producing a solid component, which is contained in saidheated exhaust gas.